The present invention relates to electrical contact probes and in particular to spring-loaded contact probes developed for use in electrical testing for a variety of applications. Such probes are generally used to provide electrical contact between diagnostic or testing equipment and an electrical device to be tested.
Conventional spring-loaded contact probes generally include a receptacle, a plunger/probe member, and a spring-loaded barrel. In such devices, the plunger/probe member is mounted in the barrel and extends outwardly therefrom. The barrel includes spring means, so that the plunger/probe member is springably supported. That is, the probe member is biased outwardly a selected distance by the spring, and may be biased or depressed inwardly of the barrel, a selected distance, under force directed against the spring. The probe member is generally provided with a head or tip that may be used to contact electrical devices to be tested. Herein, such conventional contact probes are generally referred to as three-component probes, since they have a receptacle, barrel and probe member.
In conventional devices the barrel is mounted within the receptacle, with the plunger/probe member extending outwardly from the receptacle. Preferably, the barrel is removably mounted, so that should damage occur to the barrel or probe member, replacement is possible. Usually, the receptacle is permanently or semi-permanently mounted within a matrix for use within a testing facility. Electrical wiring may be attached to the receptacle, for electrical communication between the receptacle and the testing equipment or diagnostic equipment. Preferably, the probe member, barrel and receptacle, are manufactured from electrically conductive materials, so that an electrical circuit may be maintained between an electrical device to be tested, and diagnostic equipment, by means of the contact probe.
When such electrical probes are used, generally a contact side of the electrical equipment to be tested is brought into contact with the tip of the probe member, under pressure. Under the pressure, the probe member will generally bias inwardly of the barrel, against the spring, with the spring maintaining substantial pressure to the abutment of the probe member against the electrical device. This can be accomplished by the pressing of the electrical device against a stationary probe member, or by movement of the probe member against a stationary electrical device, or movement of both, as circumstances permit.
Often in conventional systems, a plurality of contact probes may be mounted within a single matrix. Generally, two methods may be used. In a first, a plurality of contact probes are mounted in a pattern suitable for use with a selected electrical device to be tested. In a second, generally, a plurality of probes are mounted in a pattern of columns and rows, with the probes located at positions evenly spaced, for example every 0.050 inches, along the rows and columns. Each of the probes for such an arrangement is connected to the diagnostic equipment.
With the latter type of system, generally an interface is used between the array of probes and the electrical device to be tested. Such an interface generally comprises probes mounted in a pattern appropriate for the particular electrical device to be tested. That is, the electrical device will be contacted by probes of the interface, which then only contact selected probes in the matrix. Thus, if it is desired to use the same matrix for testing different devices, only the interface need be changed. In this manner, it is not necessary to wire a separate matrix to the diagnostic equipment, for each type of device to be tested.
Recently, a general problem in developing testing equipment has been in the construction of probes for use with electrical devices, having a plurality of contact points or sites to be contacted by the probes, in which the contact sites are separated from one another by only a small distance. In particular, when contact points on an electrical device are located only about 0.020 inches apart, or less, conventional contact probes have posed problems. Generally, the problems have arisen from the fact that conventional receptacle, barrel and plunger/probe assemblies, have required sufficient overall width to make spacing of probes only 0.020 inches apart quite difficult, particularly when a large number of probes are involved.
In the past, several approaches have been taken, in attempts to solve this problem. One of these has been the development of devices often referred to as "buckle beams", and a second has been the development of a two-component contact probe.
A buckle beam generally comprises a very thin, somewhat rigid, electrically conducting contact mounted upon the end of a wire. When the buckle beam is brought into contact with a device to be tested, the beam bends or buckles somewhat, giving a spring-like effect. A plurality of buckle beams may be mounted within a holder or matrix, for use in testing electrical equipment.
Generally, buckle beams have been an unsatisfactory solution. First, as the buckle beam buckles or bends it takes up a lateral width and there is some risk of contact with one of the neighboring probes. Also, such devices may be relatively difficult to mount, and once mounted may be relatively difficult to change should damage occur to the buckle beam. Further, the buckling or bending does not, generally, provide a very great spring force, so the electrical contact is not very secure. Also, such devices may not maintain their proper spacing during use, and the tip of the probe may become displaced from its proper position.
Two-component spring-loaded contact probes have been developed by Interconnect Devices, Inc., the assignee of the present invention, as a partial solution to the problem of a contact probe, for use with contact sites or centers to be tested that were spaced a very small distance, for example, 0.020 inches, apart. With such probes, the extra width required by a receptacle and barrel arrangement is generally avoided. Such probes generally include a cylinder member, springably receiving a plunger/probe member, with a tip of the probe member extending outwardly from the cylinder member. The cylinder member is generally directly connected to diagnostic equipment, by means of an electrical wire or the like. Thus, the extra width added by the receptacle and barrel arrangement is avoided, and the probes may be positioned in a matrix arrangement with relatively close spacing. Further, a wider plunger/probe member may be enabled by the relatively small overall diameter of the probe. Thus, with such devices, the plunger/probe member may be wider and longer and will be less likely to bend during use.
An initial problem with such two-component contact probes has been in their mounting. Generally, the receptacle of a conventional three-component probe is mounted within a mounting matrix by means of a friction ring or retaining ring located on an outer surface of the receptacle. A relatively permanent mounting is permissible under such circumstances, as the barrel and probe member are usually constructed to be replaceable in a mounted receptacle, when necessary.
However, with two-component contact probes, if the cylinder member were permanently or semi-permanently mounted in the matrix, the plunger/probe member could not be readily changed when necessary. Thus, a means of mounting was necessary which would permit the two-component contact probe to be easily mounted and dismounted within a matrix or holder mechanism. Further, a general method of mounting comparatively small probes, relatively easily, has been needed.
Conventional two- and three-component contact probes generally have elongate, cylindrical, outer surfaces. Such a surface, especially when as small as might be used in small spring-loaded contact probes, has not provided for ready engagement by a holder mechanism, except by means of a resistance ring or friction ring, as described above. Due to the very small size of such probes, generally the mounting of handles or the like, for engagement by some portion of a holder mechanism, is not practical. Further, some matrices, or holder mechanisms, may include thousands of probes. It will be readily seen that the holder mechanism must be relatively simple to engage, and secure in operation, in order to be practical and desirable under such circumstances.
A related problem not sufficiently addressed by prior contact probes, has been the problem of a design of a contact probe for use under circumstances where a relatively long stroke for the plunger/probe member is required. That is, when, in use, the probe member may be expected to bias a relatively great distance into the barrel or cylinder member, or when the probe member needs to be particularly long. This has been a special problem in three-component contact probes. That is, for such probes the width or lateral distance taken up by the barrel width and receptacle width has generally necessitated a relatively narrow or thin probe member. If a probe member is to be biased over a relatively great distance, against a spring, the probe member needs to be relatively wide and strong. On one hand, if the probe member is wide, the barrel and receptacle, in order to accommodate the width of the plunger/probe member, in the past have also needed to be relatively wide, thus requiring a relatively great distance between sites to be contacted. On the other hand, if the probe member is made relatively thin, the plunger/probe member may not be strong enough to resist bending or buckling during use.